Synthetic, poly-alpha-olefins (PAO), such as 1-decene oligomers, have found wide acceptability and commercial success in the lubricant field for their superiority to mineral oil-based lubricants. In terms of lubricant properties improvement, industrial research effort on synthetic lubricants has led to PAO fluids exhibiting useful viscosities over a wide range of temperatures, i.e., improved viscosity index (VI), while also showing lubricity, thermal and oxidative stability and pour point equal to or better than mineral oil.
These relatively new synthetic lubricants lower mechanical friction, enhancing mechanical efficiency over the full spectrum of mechanical loads from worm gears to traction drives, and do so over a wider range of ambient operating conditions than mineral oil. The PAO's are prepared by the polymerization of 1-alkenes using typical Lewis acid or Ziegler-catalysts. Their preparation and properties are described by J. Brennan in Ind. Eng. Chem. Prod. Res. Dev., 1980, 19, pp. 2-6. PAO incorporating improved lubricant properties are also described by J. A. Brennan in U.S. Pat. Nos. 3,382,291, 3,742,082, and 3,769,363.
In accordance with customary practice in the lubricants art, PAO's have been blended with a variety of functional chemicals, oligomeric and high polymers and other synthetic and mineral oil-based lubricants to confer or improve upon lubricant properties necessary for applications such as engine lubricants, hydraulic fluids, gear lubricants, etc. Blends and their components are described in Kirk-Othmer Encyclopedia of Chemical Technology, third edition, volume 14, pages 477-526. A particular goal in the formulation of blends is the enhancement of the viscosity index by the addition of VI improvers which are typically high molecular weight synthetic organic molecules. While effective in improving the viscosity, these VI improver have been found to be deficient in that their very property of high molecular weight, which makes them useful as VI improvers, also confers upon the blend a vulnerability in shear stability during actual use applications.
Open gear greases are used for lubrication generally of open gears and bushings, and have particular application in lubrication of, for example, boom point sheaves, crowd/retract sheave antifriction bearings, hoist drum bearings, crowd drum bearings, hoist intermediate gear cases, hoist intermediate shaft bearings, hoist motor shaft bearings and transverse shaft bearings in crawler final drive cases. Such greases have typically been based on asphalt (bitumen)/high viscosity index mineral oil blends, and it has usually been necessary to incorporate a chlorinated solvent, e.g., 1,1,1-trichloroethane, in order to facilitate low temperature mobility of the grease (to assist pumping thereof), e.g., for cold climates such as Canada or northern Europe. Once the grease is in place, the chlorinated solvent evaporates off. Since chlorinated solvents such as 1,1,1,-trichloroethane have been implicated in ozone depletion of the earth's upper atmosphere, avoidance of their use would be advantageous.
It would be advantageous to have a lubricant composition useful for base fluids for open-gear greases which did not require a viscosity improver or chlorinated solvents.